1. Field of the Invention
The invention concerns an illumination system for a surgical microscope. Quite varied illumination systems are known in microscopy. Illumination is a particularly difficult subject in surgical microscopy, and, there, especially, in ophthalmology. That is because optimal illumination can be critical for surgical success and also because the light intensity under the microscope cannot be made as high as might be desired because of danger to the tissue.
2. Description of the Related Art
German Patent C2-40 28 605 and its family member, U.S. Pat. No. 5,126,877, present a known illumination system. A still older illumination system which works well, was marketed in 1985 by the applicant""s predecessor company as xe2x80x9c0xc2x0 Illumination Systemxe2x80x9d (see the Wild Heerbrugg AG brochure M1 668d-X.85 of Oct. 1985).
In this design, the entire light beam is deflected from an illumination optical system with its lamp by a first prism, from a perpendicular to the optical axis of the main objective of the microscope into an oblique beam at a small angle (e. g., 6xc2x0) from the optical axis. This is the main illumination of the surgical field. But, to get the xe2x80x9c0xc2x0 illuminationxe2x80x9d particularly desired for eye surgery because of the xe2x80x9cred reflectionxe2x80x9d which it produces, a transparent disk parallel to the principal plane of the main objective is placed between the first prism and the main objective. This disk can be rotated about the main axis. The disk carries a second prism, which is relatively narrow in comparison with the first one. This second prism moves part of the light beam diverted by the first prism into the main axis by means of two approximately parallel mirror surfaces.
Thus, rotation of the mirror can optionally add xe2x80x9c0xc2x0 illuminationxe2x80x9d to standard illumination at a small angle to the main axis. That process reduces the light flux of the standard illumination in proportion to the light flux which it uses. Theoretically, it is possible to control the distribution of the light by the angular position about the main axis.
As well proven as this known design is, there has been a great desire for newer solutions which work without rotating disks. The solution of the German C and U.S. patents cited was noted initially as one such solution.
A significantly more recent design is reported in Japanese Patent Application 9-105866. It is somewhat comparable with the old xe2x80x9c0xc2x0 Illuminationxe2x80x9d of the predecessor of the applicant, in that it has, below the first prism, a second prism with two mirror surfaces, but it does not rotate about the main axis. This design gives a fundamentally constant division of the light flux between the 0xc2x0 portion and the larger portion that is permanently incident at a small angle. Apparently it is possible to reduce the joint light flux by a diaphragm which can be inserted into the beam path of the illumination optical system.
This Japanese design has in common with the xe2x80x9c0xc2x0 Illuminationxe2x80x9d that two prisms are placed in succession, so that both require a certain distance in front of the main objective. In addition, control of the light flux in the main axis region necessarily changes the light flux which is incident on the object at a small angle.
One of those effects, and preferably the other also, are intended to be avoided according to the invention.
The object of the invention, then, is to provide a compact illumination system with at least one oblique (with respect to the main axis) light flux and at least one parallel light flux, so that as much as possible the two light fluxes can be controlled independently of each other.
This object is attained, for the first time, by an illumination system according to the present invention. The illumination system generally comprises an illumination means for providing an illumination beam of light along an illumination optical axis, and a plurality of prisms located to receive and divert respective portions of the illumination beam through the objective lens of the microscope either along the main optical axis of the objective lens or at a small angle relative thereto.
An elegant solution with symmetric illumination of the object includes a central prism for diverting a portion of the illumination beam along the main optical axis, and a pair of prisms located on each opposite side of the central prism for diverting portions of the illumination beam at a small angle to the main optical axis, wherein the three prisms have a combined light entry surface area facing the illumination beam that essentially admits the entire illumination beam when unblocked.
The present invention gives a small height, as the prisms are now side by side. It also assures that the light entry areas of the two prisms can be supplied with a partial flux of light independently of each other, so that each of these partial light fluxes can be controlled independently of the other.
Placing an adjustable diaphragm between the illumination optical system and at least one light entry surface of at least one prism presents an example of one such potential for regulation. Adjustable diaphragms such as an opaque disk with windows which can be selectively placed so as to allow the illumination beam to enter different light entry surfaces to different extents, as needed, are simply adjustable diaphragms. An LCD which, under electronic control, allows freely selectable portions to enter the light entry surfaces is a particularly user-friendly diaphragm. LCDs can be used as gray filters by selective darkening. On the other hand, electronically stored window shapes can be used to provide quite varied illumination adjustments.
The invention is not limited to these stated diaphragms, though. It can instead be equipped with any known or novel system for light control without losing its essential feature, the flat, compact design and the ability to control independently.
In a particular embodiment and possibly an alternative to those described previously, at least one light-interrupting part is positioned at at least one of the reflective surfaces of the prisms, in such a way that the light-interrupting part can be moved or swiveled with electronic means, or can be electro-optically controlled so as to refract the total reflection. It can reasonably be used alternatively or even in combination. If needed, it also leads to an improved and even more symmetric illumination.
The term xe2x80x9clight-interrupting partxe2x80x9d is understood to mean any element in which total reflection is eliminated at the contact site when in contact with a total reflection surface. They could, for example, be prisms, glass plates, or even certain, possibly non-transparent, plastic or metal plates or liquids. This particular embodiment provides not only the possibility for light control, but also the possibility for dividing a light flux for use of another optional mirror element to produce another illumination beam at an angle to the main axis. There is another preferred embodiment in which only the xe2x80x9c0xc2x0 Illuminationxe2x80x9d is controlled by using the interruption of total reflection or, in case the light flux is diverted out of the second prism, it is directed to another oblique illumination beam independent of the first oblique illumination beam.
According to the invention, a means for controlling the color of the light can also be provided, independently of, or in addition to, the light flux regulation.